18/10/16 START: 16:56
18/10/17 STOP: 9:51

ROOT file: 181017_0951_BkgOverNight.root

Comment:
Tube 121 is noisier than the others (see fig).

Issue:
all the channels connected to PA3 and PA4 
have twice the number of counts than the remaining channels (!?).
Actually the pulser counts.

Solution:
This channels are from UPC tubes and are connected to pulser PB-5.
We found that the threshold of external trigger was set to 1V
instead to 1.8V as before and this was producing a double pulse (see photo)
like triggering on the fall and rise of the trigger pulse.
This happen whenever the threshold as below 1.6V.
We do not understand this: the signal has +2.2V and no apparent ripple (!????).
We set threshold to 1.8V and now is OK